1. Field of the Invention
This invention relates to an assembly, method and system for reducing fan noise from a noise-generating system such as a turbofan engine. More particularly, this invention relates to an assembly comprising at least one dynamically adaptable Herschel-Quincke (HQ) tube which is capable of being dynamically adapted with respect to tube geometry and acoustical characteristics to optimize cancellation of the predominant source tone for different engine cycles. The method and system of this invention employ such an assembly to reduce fan noise from noise-generating systems such as turbofan aircraft engines.
2. Background Information
The desirability of reducing the noise generated by aircraft engines such as turbofan engines is well known to those skilled in the art. As disclosed, for example, in U.S. Pat. No. 6,112,514, which is incorporated herein by reference in its entirety, one method of reducing such noise which has been proposed is the use of Herschel-Quincke tubes of appropriate length arranged in an array about a turbofan engine to reduce the noise levels generated by the engine. Such an array of tubes, if properly located about the engine, create destructive energy waves that cancel the acoustic energy in the turbofan engine yet do not contribute to any significant aircraft drag or reduced fuel consumption. As is also disclosed in U.S. Pat. No. 6,112,514, various parameters such as tube length, cross-sectional area etc. may be controlled via a control system responsive to varying engine operational or environmental conditions. In such a control system sound is reintroduced into the system in an out-of-phase relation from the sound propagating from the engine fan to effect sound cancellation. Such a control system may employ feedback or feedforward control, or a combination thereof.
However, it is also known that engine noise tones tend to wander in frequency due to atmospheric conditions or engine cycle settings. Accordingly, it would be desirable to dynamically actuate changes in the tube design parameters in conjunction with a control system employing feedback or feedforward control, or a combination thereof.
It is one object of this invention to provide an assembly comprising one or more dynamically adaptable Herschel-Quincke tubes which is capable of being dynamically adapted with respect to tube geometry and acoustical characteristics to optimize noise reduction in a turbofan engine. The assembly of this invention advantageously permits the tubes to be dynamically actuated in cooperation with a feedback or feedforward control system, or combination thereof, to optimize the noise cancellation effect of the assembly. It is another object of this invention to provide a method which employs such an assembly to reduce fan noise from noise-generating systems such as turbofan aircraft engines. It is yet another object of this invention to provide a system which employs such an assembly to reduce fan noise from noise-generating systems such as turbofan aircraft engines. Other objects, features and advantages of the invention will be apparent to those skilled in the art from the detailed description of the invention and its various embodiments as described herein.